Our overall goal is to demonstrate, on amputees, the feasibility of controlling a four degree-of-freedom prosthetic arm using the small electrical signals (EMG) which are generated by the amputee's remnant shoulder and stump musculature. An associated goal is to generate missing quantitative biomechanical information which is necessary for implementation of our limb controller as well as useful to other interested researchers. During our present grant we have achieved significant results. We have demonstrated the promise of the Postulate based control method via over 100 experiments utilizing 9 volunteer amputees. We have achieved proportional, reliable, and easy-to-use simultaneous control of humeral rotation and elbow flexion. Significant progress has also been realized toward the control of wrist rotation and prehension. We have developed a comprehensive experimental facility capable of gathering static and dynamic neuromuscular data on human subjects and have accomplished much toward the quantification of knowledge in the following areas: (1) musculoskeletal anatomy, (2) the relationship between muscularly generated torques about joints and cutaneously measured EMG signals, (3) patterns of coordination of multiple redundant muscles of the arm and shoulder, and (4) methods for processing EMG signals to permit more reliable prosthesis control. Our experimental facility includes a high performance, computer-controlled, four degree-of-freedom prosthesis which can be utilized on fully mobile amputees. These devices are extremely valuable tools for the development and evaluation of control methodologies. Our goal is to complete efforts devoted to the control of wrist rotation and prehension using the Postulate based method and other methods. We also intend to refine the four degree-of-freedom control system through extensive evaluations in the laboratory and the amputee's home, work and recreational environments. The quantification of fundamental biomechanical knowledge will continue to be a goal of the project and we intend to complete work in the four areas mentioned above.